The present invention relates to hydrofluorocarbons, and more particularly, to hydrofluorocarbon solvents having a portion which is fluorocarbon and the remaining portion is hydrocarbon.
Vapor degreasing and solvent cleaning with fluorocarbon based solvents have found widespread use in industry for the degreasing and otherwise cleaning of solid surfaces, especially intricate parts and difficult to remove soils.
In its simplest form, vapor degreasing or solvent cleaning consists of exposing a room-temperature object to be cleaned to the vapors of a boiling solvent. Vapors condensing on the object provide clean distilled solvent to wash away grease or other contamination. Final evaporation of solvent from the object leaves behind no residue as would be the case where the object is simply washed in liquid solvent.
For difficult to remove soils where elevated temperature is necessary to improve the cleaning action of the solvent, or for large volume assembly line operations where the cleaning of metal parts and assemblies must be done efficiently and quickly, the conventional operation of a vapor degreaser consists of immersing the part to be cleaned in a sump of boiling solvent which removes the bulk of the soil, thereafter immersing the part in a sump containing freshly distilled solvent near room temperature, and finally exposing the part to solvent vapors over the boiling sump which condense on the cleaned part. In addition, the part can also be sprayed with distilled solvent before final rinsing.
Vapor degreasers suitable in the above-described operations are well known in the act. For example, Sherliker et al. in U.S. Pat. No. 3,085,918 disclose such suitable vapor degreasers comprising a boiling sump, a clean sump, a water separator, and other ancilliary equipment.
Cold cleaning is another application where a number of solvents are used. In most cold cleaning applications, the soiled part is either immersed in the fluid or wiped with rags or similar objects soaked in solvents.
Chlorofluorocarbon solvents, such as trichlorotrifluoroethane, have attained widespread use in recent years as effective, nontoxic, and nonflammable agents useful in degreasing and other solvent cleaning applications. Trichlorotrifluoroethane has been found to have satisfactory solvent power for greases, oils, waxes, and the like. It has therefore found widespread use for cleaning electric motors, compressors, heavy metal parts, delicate precision metal parts, printed circuit boards, gyroscopes, guidance systems, aerospace and missile hardware, aluminum parts, and the like. Trichlorotrifluoroethane has two isomers: 1,1,2-trichloro-1,2,2-trifluoroethane (known in the art as CFC-113) and 1,1,1-trichloro-2,2,2-trifluoroethane (known in the art as CFC-113a).
Chlorofluorocarbons such as CFC-113 are suspected of causing environmental problems in connection with the ozone layer. In response to the need for stratospherically safe materials, substitutes have been developed and continue to be developed. For example, commonly assigned U.S. Pat. No. 4,947,881 teaches a method of cleaning using hydrochlorofluorocarbons having 2 chlorine atoms and a difluoromethylene group.
A need exists in the art for a class of solvents which have zero ozone depletion potentials, have boiling point ranges suitable for a variety of solvent applications, and have the ability to dissolve both hydrocarbon based and fluorocarbon based soils. From an environmental standpoint, hydrocarbons (compounds having hydrogen and carbon), fluorocarbons (compounds having fluorine and carbon), and hydrofluorocarbons (compounds having hydrogen, fluorine, and carbon) are of interest because they are considered to be stratospherically safe substitutes for the currently used CFCs.
G. Giacometti et al., "The Gas Phase Reactions of Perfluoro-n-propyl Radicals with Methane and Ethane," Canadian Journal of Chemistry, 36, 1493 (1958) teach a method for the preparation of C.sub.5 F.sub.7 H.sub.5 but do not teach or suggest that it would be useful as a solvent.
R. H. Groth, "Fluorinated Paraffins", J. Org. Chem. 24, 1709 (1959) teaches a method for the preparation of C.sub.3 F.sub.7 C.sub.3 H.sub.7 but does not teach or suggest that it would be useful as a solvent.
Yung K. Kim et al., "Isomeric 2,4,6-Tris(3,3,4,4,5,5,6,6,6-nonafluorohexyl)-2,4,6-trimethylcyclotrisilox anes", J. Org. Chem. 38(8), 1615(1973) teach a method for the preparation of 1,1,1,2,2,3,3,4,4-nonafluorohexane but do not teach or suggest that it would be useful as a solvent.
European Patent Publication 381,986 published Aug. 16, 1990 teaches hydrofluorocarbons having 3 to 6 carbon atoms.
The problem with hydrocarbon solvents is that although they are excellent solvents for hydrocarbon solutes as shown in Comparative G in Table V below, they have limited ability to dissolve highly fluorinated solutes. The problem with fluorocarbon solvents is that although they are excellent solvents for fluorocarbon solutes such as perfluorinated ethers, they are very poor solvents for hydrocarbons as shown in Comparative L in Table V below.
Turning to hydrofluorocarbons, we tested potential solvents for their ability to dissolve, in order of decreasing molecular weight: (a) hydrocarbons: paraffinic light mineral oil (maximum Saybolt viscosity 158), hexadecane (molecular weight 226), dodecane (molecular weight 170), decane (molecular weight 142), octane (molecular weight 114), heptane (molecular weight 100), and hexane (molecular weight 86) and (b) fluorocarbon: perfluorinated polyether (molecular weight 3500). The hydrocarbon listed in the tables below for each comparative and example is the maximum weight hydrocarbon that was miscible with (a 1:1 volume ratio of solute and solvent were homogeneous) the comparative or example.
We found that although mineral oil solute is miscible with hydrofluorocarbon solvents such as CH.sub.3 CH.sub.2 CF.sub.2 CH.sub.2 CH.sub.3 as shown in Comparative H in Table V below, the perfluorinated polyether solute is insoluble in CH.sub.3 CH.sub.2 CF.sub.2 CH.sub.2 CH.sub.3 and CH.sub.2 FCH.sub.2 CH.sub.2 F solvents as shown in Comparatives H and M in Table VII below and thus, CH.sub.3 CH.sub.2 CF.sub.2 CH.sub.2 CH.sub.3 and CH.sub.2 FCH.sub.2 CH.sub.2 F are unsuitable for use as solvents with both hydrocarbon and fluorocarbon solutes.
Relative to hydrofluoropentane solvents, we found that mineral oil solute is miscible with CH.sub.3 (CF.sub.2).sub.2 CH.sub.2 CH.sub.3 which has 53 weight percent fluorine as shown in Comparative F in Table V below. We found that dodecane solute is miscible with each of the following solvents: CH.sub.3 CF.sub.2 CH.sub.2 CF.sub.2 CH.sub.3 which has 53 weight percent fluorine, CH.sub.3 (CF.sub.2).sub.3 CH.sub.3 which has 63 weight percent fluorine, and CF.sub.3 (CH.sub.3 )CHCH.sub.2 CF.sub.3 which has 63 weight percent fluorine, as shown in Comparatives A, E, and I respectively in Table V below. We found that decane is miscible with HCF.sub.2 CF.sub.2 CH.sub.2 CH.sub.2 CF.sub.3 which has 67 weight percent fluorine as shown in Comparative J in Table V below. We found that octane solute is miscible with CF.sub.3 CH.sub.2 CH(CF.sub.3 ).sub.2 which has 73 weight percent fluorine as shown in comparative K in Table V below. We found that hexane solute is miscible with CF.sub.3 CH.sub.2 CF.sub.2 CH.sub.2 CF.sub.3 which has 70 weight percent fluorine as shown in Comparative B in Table V below.
Relative to hydrofluorohexane solvents, we found that decane solute is miscible with each of the following solvents: CF.sub.3 (CF.sub.2).sub.2 CH.sub.2 CHFCH.sub.3 which has 66 weight percent fluorine as shown in comparative C in Table VI below.